Startup schematic

Figure 4-74. Typical startup schematic for turboexpanders in FCC units.

During cell/stack operation, water content in the membrane is affected by the local intensive variables, such as local temperature, water vapor concentration in the gas phase, gas temperature and velocity in the channel, and the properties of the electrode and gas diffusion media. The power fluctuation can result in temperature variation inside the cell/stack, which will subsequently change the local membrane water content. As the water content in the membrane tends to be non-uniform and unsteady, this results in operation stresses. When the membrane uptakes water from a dry state, it tends to expand as there is no space for it to extend in plane and it can wrinkle up as schematically shown in Fig. 4 when the membrane dries out, the wrinkled part may not flatten out, and this ratcheting effect can cause the pile up of wrinkles at regions where membrane can find space to fold. The operation stress is typically cyclic in nature due to startup-shutdown cycles, freeze-thaw cycles, and power output cycles. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

In some cases, construction and startup are separate phases of a project and are not included in final engineering. In oil packaging projects, this is normally part of the final phase. Thus, concise definition and agreement on the contents of final schematics and specifications cannot be overestimated, as both system capability and overall project cost can be traced to this definition. 

Figure 3.92 is a process schematic of the world s largest cheese plant (at time of startup in 1985) in Corona, California. The plant utilizes many of the processes described above producing 5 million Ib/year of WPC (by UF) (50 to 75% protein) and 2.2 million gal/year of ethanol for gasohol. The lactose permeate from the UF unit is concentrated by RO before use as a fermentation medium to produce alcohol. 

Shutdown/startup of the reactor would be achieved by control elements in the radial reflector, outside the core clad. The reactor coolant outlet temperature/turbine inlet temperature is 900 K. A simplified schematic of this reactor concept is presented below. 

Figure A5.11 Schematic of RDIPE SCW NPP (1) reactor (4) preheating channel (5) first SHS (6) second SHS (11) condensate extraction pump (14) deaerator (15) turbo-generator (17) condenser (18) condenser purifier (19) mixer (20) startup separator (21) intermediate steam reheater (22) low-pressure regenerative preheater (23) high-pressure regenerative preheater (24) feed turbo-pump and (25) booster pump.

The redesigned system is schematically described in Fig. 5.69. The startup bypass system in the original design is replaced by the separate recirculation system that consists of a steam drum, a heat exchanger, a circulation pump, and pipes. Neither the inlet nor outlet of the recirculation system are connected to the main lines, rather they are directly connected to the reactor vessel in order to form a closed space for pressurization like the recirculation system of BWRs. 

The startup procedures are redesigned in detail, referring to LWRs and FPPs. The coolant flow paths during these procedures are schematically described in Figs. 5.70-5.74 as red lines. 

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